In the title compound, C33H25F2NO2, the acenaphthene ring system forms dihedral angles of 50.93 (14) and 36.89 (14)° with the benzene rings. The pyrrolidine and cyclopentanone rings adopt envelope (with the N atom as the flap) and twisted conformations, respectively. In the crystal, C-HO and C-HF interactions link the molecules.

The bond lengths and angles in the pyrrolidine ring are slightly larger than
normal values because of bulky substituents on the pyrrolidine moiety. A
similar effect has been observed in related reported structures (Abdul Ajees
et al., 2002; Usha et al., 2003). The sum of the
angles
at atom N1 [339.1 (11)°] is in accordance with sp3-hybridization.
The dihedral angles between the acenaphthene ring system and phenyl rings
C21—C26 and C27—C32 are 50.93 (14)° and 36.89 (14)° respectively, while
that between the two phenyl-ring substituents is 87.55 (17)°. The pyrrolidine
and cyclopentanone ring both adopt an envelope conformation. In addition to
van der Waals interactions, the crystal structure is stabilized by C—H···O
and C—H···F intramolecular interactions. In the present study, the
1,3-dipolar cycloaddition of an azomethine ylide generated in situ
from acenaphthenequinone and sarcosine to novel mono-carbonyl analogue of
curcumin containg cyclopentanone afforded title compound.

A mixture of (2E,5E)-2,5-bis(2-fluorobenzylidene)cyclopentanone (1 mmol),
(Liang et al., 2009), acenaphthenequinone (0.182 g, 1 mmol), and
sarcosine (0.089 g, 1 mmol) was dissolved in methanol (10 mL) and refluxed
for 1 h. After completion of the reaction as evident from TLC, the mixture
was cooled to room temperature and poured into cold water (50 mL). The
precipitate was filtered and washed with water to obtain pure product as a
yellow solid (79.6% yield, mp 93.2–95.0°C). Single crystals were grown in
an ethyl acetate/CH2Cl2 mixture (2:1ν/ν).

The H(C) atom positions were calculated. The H atoms bound to C were positioned
geometrically and allowed to ride on their parent atoms at distances of
0.96 Å (RCH3), 0.97 Å (R2CH2), 0.98 Å (R3CH), 0.93 Å (R2CH),
and with Uiso(H) values set to either 1.2Ueq or 1.5Ueq (RCH3) of the
attached atom.

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell esds are taken
into account individually in the estimation of esds in distances, angles
and torsion angles; correlations between esds in cell parameters are only
used when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell esds is used for estimating esds involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor
wR and goodness of fit S are based on F2, conventional
R-factors R are based on F, with F set to zero for
negative F2. The threshold expression of F2 >
σ(F2) is used only for calculating R-factors(gt) etc.
and is not relevant to the choice of reflections for refinement.
R-factors based on F2 are statistically about twice as large
as those based on F, and R- factors based on ALL data will be
even larger.

This work was supported by the Zhejiang Provincial Natural Science Foundation
of China (grant Nos. LY12H16003 and Y4110197) and the Project of Wenzhou
Science & Technology Bureau (Y20100273). The X-ray crystallographic facility
at the Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
is gratefully acknowledged for the data collection.